Engine driven by Sc02 cycle with independent shafts for combustion cycle elements and propulsion elements

ABSTRACT

A gas turbine engine includes a first shaft coupled to a first turbine and a first compressor, a second shaft coupled to a second turbine and a second compressor, and a third shaft coupled to a third turbine and a fan assembly. The turbine engine includes a heat rejection heat exchanger configured to reject heat from a closed loop system with air passed from the fan assembly, and a combustor positioned to receive compressed air from the second compressor as a core stream. The closed-loop system includes the first, second, and third turbines and the first compressor and receives energy input from the combustor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of non-provisionalapplication Ser. No. 15/185,498, filed Jun. 17, 2016, which claimspriority to U.S. Provisional Application No. 62/181,887 filed Jun. 19,2015, which are hereby incorporated by reference in their entirety.

FIELD OF TECHNOLOGY

An improved apparatus and method of operating a gas turbine engineincludes providing power to a shaft of the gas turbine engine usingcarbon dioxide (CO₂) operated in super-critical cycle.

BACKGROUND

It has become increasingly desirable to reduce the size ofpower-producing or thrust-producing devices such as gas turbine engines.Gas turbine engines typically include one or more shafts that includecompressors, bypass fans, and turbines. Typically, air is forced intothe engine and passed into a compressor. The compressed air is passed toa combustor, and at high temperature and pressure the combustionproducts are passed into a turbine. The turbine provides power to theshaft, which in turn provides the power to the compressor and bypass fanor gearbox. Thrust is thereby produced from the air that passes from thebypass fan, as well as from the thrust expended in the turbinecombustion products.

However, air can be thermodynamically inefficient, especially duringcruise operation of the engine (such as in an aircraft). Air that entersthe engine is of low pressure, therefore low density. In order to reachthe needed pressure and temperature at the combustor exit, the air iscompressed to very high pressure ratios and heated up to very hightemperatures in the combustors. In order to provide adequate mass flowrate, significant volume flow rate of the low density air is pumpedthrough high pressure ratio consuming significant amount of power. As aresult the engines are made of large and heavy components, consume largeamount to fuel, and may include significant operational and maintenanceexpenses to cope with high combustion temperatures.

To reduce component size and complexity, some power-producing orthrust-producing devices include a super-critical carbon dioxide (s-CO₂)system that provides significantly improved efficiencies compared toBrayton and other air-based systems by operating in a super-criticalregion (operating at a temperature and pressure that exceed the criticalpoint). That is, a phase-diagram of CO₂, as is commonly known, includesa “triple point” as the point that defines the temperature and pressurewhere solid, liquid, and vapor meet. Above the triple point the fluidcan exist in liquid, vapor, or in a mixture of the both states. However,at higher temperature and pressure, a critical point is reached whichdefines a temperature and pressure where gas, liquid, and asuper-critical region occur. The critical point is the top of the domemade up of the saturated liquid and saturated vapor lines. Above thecritical point is the gaseous region.

Fluids have a triple point, a critical point, saturated liquid and vaporlines, and a super-critical region. One in particular, carbon dioxide,is particularly attractive for such operation due to its criticaltemperature and pressure of approximately 31° C. and 73 atmospheres,respectively, as well as due to its lack of toxicity. Thus, s-CO₂— basedsystems may be operated having very dense super-critical properties,such as approximately 460 kg/m³. The excellent combination of thethermodynamic properties of carbon dioxide may result in improvedoverall thermodynamic efficiency and therefore a tremendously reducedsystem size. Due to the compact nature and high power density of a powersource that is powered with a super-critical cycle, the overall size ofengine may be significantly reduced, as well.

A super-critical fluid occurs at temperatures and pressures above thecritical point, where distinct liquid and gas phases do not exist. Closeto the critical point and in the super-critical region, small changes inpressure or temperature result in large changes in density, allowingmany properties of the super-critical fluid to be fine-tuned, providinga tremendous opportunity for high power energy extraction and in a smallfootprint relative to, for instance, an air-based thermodynamic system(such as a Brayton cycle).

However, rotational speeds for each component within known engines arenot necessarily optimized, and thus overall system efficiency is not atits peak. As such, there is a need to provide system operation inpower-producing devices that employ a s-CO₂ operation.

BRIEF DESCRIPTION OF THE DRAWINGS

While the claims are not limited to a specific illustration, anappreciation of the various aspects is best gained through a discussionof various examples thereof. Referring now to the drawings, exemplaryillustrations are shown in detail. Although the drawings represent theillustrations, the drawings are not necessarily to scale and certainfeatures may be exaggerated to better illustrate and explain aninnovative aspect of an example. Further, the exemplary illustrationsdescribed herein are not intended to be exhaustive or otherwise limitingor restricted to the precise form and configuration shown in thedrawings and disclosed in the following detailed description. Exemplaryillustrations are described in detail by referring to the drawings asfollows:

FIG. 1 is an illustration of a conventional gas turbine engine;

FIG. 2 is an illustration of an exemplary gas turbine having a turbofanand multiple rotational shafts and a closed-loop system power-producingcircuit that includes its own working fluid, such as a s-CO₂ system;

FIG. 3 is an illustration of an exemplary gas turbine having multiplerotational shafts and a two-stage fan on independent shafts;

FIG. 4 is an illustration of an exemplary gas turbine having an inclinedheat rejection heat exchanger;

FIG. 5 is an illustration of an exemplary gas turbine having arecuperative heat exchanger;

FIG. 6 is an illustration of an exemplary gas turbine having apre-compression compressor; and

FIG. 7 is an illustration of an exemplary gas turbine having anadditional gearbox driven by a working fluid.

FIG. 8 illustrates an exemplary gas turbine having a turbopropconfiguration.

DETAILED DESCRIPTION

An exemplary gas turbine engine is described herein, and variousembodiments thereof. According to the disclosure, a gas turbine engineuses a power source to provide power to the shaft, while providingadequate power and thrust for aircraft and other purposes.

Various applications include, as examples, a turbojet, a turbofan,adaptable, turboprop and turboshaft engine configurations. The turbojetderives most of its thrust from the core stream and is generally mostadvantageous in high altitude and/or high mach regimes. Turbojets bypassminimal airflow around the core so they tend to be smaller diameter,noisy and drag efficient. The turbofan, on the other hand, derives mostof its thrust from the bypass stream which offers advantages in fuelsavings mostly in subsonic applications. Turbofans bypass a high amountof airflow around the core and appear larger in diameter. Because of thelarger fan turning more slowly they produce less noise than a turbojet.

A variant of the above turbine technologies is another potentialapplication. An adaptable engine, capable of varying the core/bypasssplit should also be included in the application of s-CO₂. Varying thebypass ratio might be accomplished by varying duct areas at inlets orexits to the core and bypass streams. An application such as this allowsfor both turbojet and turbofan operation so that fuel consumption can beminimized in both subsonic and supersonic regimes.

Turboprop engines characteristically attach a turbine engine to drive apropeller instead of a fan. Because propellers typically turn moreslowly because of their larger diameter, a gearbox may be providedbetween the turbine engine and the propeller. In a turboshaftapplication, the turbine connects to something other than a fan orpropeller, often a helicopter rotor or shaft in a marine application.Turboshafts typically include a gearbox between the turbine engine androtor or shaft.

FIG. 1 illustrates an exemplary schematic diagram of a gas turbinemachine 10 that is a primary mover or thrust source for an aircraft. Theturbine machine 10 includes a primary compressor 12, a combustor 14 anda primary turbine assembly 16. A fan 18 includes a nosecone assembly 20,blade members 22 and a fan casing 24. The blade members 22 direct lowpressure air to a bypass flow path 26 and to the compressor intake 28,which in turn provides airflow to compressor 12. The engine provides twomajor functions: propulsion and power generation used to rotate thecompressors, turbines, and the bypass fan. The major function,propulsion, includes fairly low air pressures and temperatures, whichare approximately equal to the pressures and temperatures exiting thegas turbine engine. However, the air pressure ratios and temperaturesgenerated in the gas turbine engine are relatively very high. The highpressure ratios and temperatures are needed to provide the powergeneration function. In one known example, an engine has a pressure of180 psia and a temperature of 1600° F. at the combustor exit andpressure of 25 psia and temperature of 1000° F. at the last turbine exitprovided that the pressure at the engine inlet is 15 psia. This meansthat the propulsion requires pressure ratio of 25/15=1.67, when thetotal pressure ratio in the engine is 180/15=12 covers power for bothpropulsion and power generation devices. In some known engines thedifference in pressure ratios and combustion temperatures may be evengreater.

A closed-loop system in this regard refers to a power-producing circuitthat includes its own working fluid, such as a s-CO₂ system, and whichoperates in compression, expansion, and heat rejection in a closed-loopanalogous to a closed-loop refrigeration system. That is, aside fromincidental leakage of the working fluid, the working fluid does nototherwise contact the external environment during operation.

Thus, in general, a power-producing device includes an inner housing forpassing a core stream of air, the inner housing houses a first shaftcoupled to a first turbine and a first compressor, a second shaftcoupled to a second turbine and a second compressor, a third shaftcoupled to a third turbine and a fan assembly, a combustor positioned toreceive compressed air from the second compressor, and a heat rejectionheat exchanger configured to reject heat from a closed loop system. Theclosed-loop system includes the first, second, and third turbines andthe first compressor and receives energy input from the combustor.

FIG. 2 is an illustration of an exemplary gas turbine or turbofan 200having multiple rotational shafts and a closed-loop systempower-producing circuit that includes its own working fluid, such as as-CO₂ system. Turbofan 200 includes a first shaft 202 coupled to a firstturbine 204 and a first compressor 206. A second shaft 208 is coupled toa second turbine 210 and a second compressor 212. A third shaft 214 iscoupled to a third turbine 216 and a fan assembly 218. A heat rejectionheat exchanger 220 is configured to reject heat from a closed loopsystem 222 with air passed from fan assembly 218. In one exampleclosed-loop system 222 includes carbon dioxide as a working fluid and isconfigured to operate as a super-critical (s-CO₂) system. A combustor224 is positioned to receive compressed air from the second compressor212 as a core stream 226. The closed-loop system 222 includes the first,second, and third turbines 204, 210, 216 and the first compressor 212,and receives energy input from the combustor 224. A bypass airflow 228is also generated from fan assembly 218, causing air to flow across heatrejection heat exchanger 220, and combustion products from combustor 224(resulting from combustion that results in part from core stream 226)and bypass airflow 228 both produce a thrust 230 for turbofan 200.

First compressor 206 of closed-loop system 222 is coupled to shaft 202for compressing the working fluid, and turbine 204 expands the workingfluid to extract the power therefrom. In operation, combustor 224provides power input to the working fluid of closed-loop system 222,which in turn is expanded (and energy extracted therefrom) by turbines204, 210, 216 before heat is rejected in heat rejection heat exchanger220. The working fluid is compressed in compressor 206 before enteringcombustor 224.

Operation of the components within closed loop system 222 may beoptimized by maximizing component efficiency by tailoring rotationalspeeds of each. For instance, fan assembly 218 typically operates at aspeed much lower than that of compressors and turbines. In addition,however, compressor 212 operates to compress air for core stream 226 forcombustion in combustor 224. Whereas compressor 206 is withinclosed-loop system 222 and is therefore configured to compress carbondioxide as closed-loop system 222 operates in super-critical mode.Accordingly, first, the second, and the third shafts 202, 208, 214 areseparately operable at different speeds from one another, and thereforeoperable according to their respective optimal design speeds. Further,according to one example, although shaft 214 coupled to fan assembly 218is separately operable, a rotational speed of fan assembly 218 may befurther reduced by use a gear 230 that is coupled between shaft 214 andfan assembly 218. Accordingly, gear 230 reduces a rotation of a fanblade within the fan blade assembly relative to a rotational speed ofthe shaft 214.

Turbofan 200 includes an inner housing 232 that houses at least aportion of the first, second, and third shafts 202, 208, 214, and passesair therethrough from fan assembly 218 to combustor 224, and bypass air228 passes from fan assembly 128 and as bypass air 228 passingexternally to inner housing 232 to provide cooling to heat rejectionheat exchanger 220. Thrust is thereby provided from both combustionbyproducts from combustor 224 and from bypass air 228.

Thus, FIG. 2 illustrates a s-CO₂ driven turbofan with independentlydriven compression and propulsion devices. There are two compressiondevices illustrated in this cycle: a low pressure (LP) compressor 212and s-CO₂ compressor 204. Compressor 212 provides core air 226 tocombustor 224 and s-CO₂ compressor 206 provides the pressure rise whichdrives the s-CO₂ power cycle. The propulsion element is a single stagefan assembly 218 which provides aircraft thrust as well as provides airflow across the heat exchange to the support power cycle.

This engine employs a sCO₂ power generation system. It includes a CO₂compressor, a heat absorption heat exchanger integrated with thecombustor, an expander, and the heat rejection exchanger built-in in theannular cross-section shaped by the nacelle and the baffle. The CO₂compressor, the CO₂ expander, the fan assembly, and the air compressorare placed on the same shaft. The net power generated by the s-CO₂ cycleis used to drive the fan and the low pressure air compressor.

With each of these devices operating on an independent shaft, the taskof speed matching for each of the devices is simplified. The speed foreach compressor/turbine or fan/turbine shaft can be selected to optimizethe performance of each set of components. This will lead to a moreflexibility in propulsion system design and a more efficient s-CO₂cycle.

FIG. 3 is an illustration of an exemplary gas turbine 300 havingmultiple rotational shafts and a two-stage fan on independent shafts.Gas turbine 300 includes components and is generally operated asdescribed with respect to FIG. 2, but further includes a fourth shaft302 having a fourth turbine 304 and a fan assembly 306 coupled thereto.A baffle 308 is positioned between an inner housing 310 and an outersurface or nacelle 312 of gas turbine engine 300. A closed-loop system314 includes fourth turbine 304. Fan assembly 306 and a fan assembly 318provide air via multiple paths to gas turbine 200. As shown, fanassembly 318 (analogous to fan assembly 218 of FIG. 2) includes a fanblade having a radius that extends proximate to outer surface 312, whilefan assembly 306 includes a fan blade having a radius that is less thanthat of the fan blade in fan assembly 318. In such fashion, both fanassemblies 306, 318 provide bypass air 316 as thrust air that passesbetween baffle 308 and inner housing 310. Both fan assemblies 306, 318also provide a core airstream 320 as core air for compression andcombustion, providing thrust via combustion byproducts. Fan assembly318, having a greater fan blade radius than that in fan assembly 306,also provides a cooling stream of air 322 that passes between baffle 308and outer surface 312, providing cooling to closed-loop system 314. Inone example, fan assembly 306 includes a gear reduction gear 324 forreducing rotation of the fan blade of fan blade assembly 306, relativeto its shaft 302.

FIG. 4 is an illustration of an exemplary gas turbine 400 having aninclined heat rejection heat exchanger 402 that increases a face areaand reduces air-side pressure drop. Gas turbine 400 is configured andoperates comparably to gas turbine 300 of FIG. 3, but in this exampleheat rejection heat exchanger 402 is positioned at an angle 404 withrespect to a central axis 406 of gas turbine 400. To accommodate heatrejection heat exchanger 402, outer surface 408 and baffle 410 aredesigned, accordingly, such that cooling air 412 passes from fanassembly 414, while both fan assemblies 414 and 416 provide core streamof air 418 and bypass air 420. Accordingly, heat transfer within heatexchanger 402 is enhanced due to an increased amount of turbulencewithin stream 412 that occurs as the air passes through and along heatexchanger 402.

FIG. 5 is an illustration of an exemplary gas turbine 500 having arecuperative heat exchanger 502. Gas turbine 500 is configured andoperates comparably to that of FIG. 4, while further includingrecuperative heat exchanger 502 that exchanges heat from the workingfluid of the closed-loop system between an outlet 504 of turbine 506 andan input 508 to the combustor. Overall system efficiency is therebyimproved, as the working fluid is cooled in recuperative heat exchanger502 prior to entering the combustor, and the working fluid is heated inrecuperative heat exchanger 502 prior to entering the heat rejectionheat exchanger. The added recuperative heat exchanger improves thethermodynamic efficiency of the power generation option.

FIG. 6 is an illustration of an exemplary gas turbine 600 having apre-compression compressor 602, and a low temperature recuperative heatexchanger 604 and a high temperature recuperative heat exchanger 606.Gas turbine 600 is otherwise configured and operates comparably to thatof FIG. 5. Overall system efficiency is thereby improved, as the workingfluid is pre-compressed in pre-compression compressor 602, and bothrecuperative heat exchangers 604, 606 further exchange heat throughoutthe process after pre-compression and after primary compression incompressor 608.

FIGS. 7 and 8 illustrate exemplary gas turbines 700 and 800 having anadditional gearbox 702, 802 driven by the working fluid, as illustrated.Turboshaft 700 and turboprop 800 configurations can utilize similar coretechnologies as the turbofan discussed earlier. These configurations areillustrated with a base core s-CO₂ cycle in FIGS. 7 and 8. Both areillustrated with a respective gear box 702, 802. However, the presenceof the gearbox depends on the load speed requirements, as well asgearbox and turbine sizing.

Thus, in operation, a method of providing power via a gas turbine engineincludes powering a first shaft via a closed loop system that passes aworking fluid from a first compressor to a combustor, receives powerfrom combustion in the combustor, passes the working fluid from thecombustor to a first turbine, and cools the working fluid in a heatrejection heat exchanger, powering a second shaft using a second turbineof the closed loop system that is coupled to the second shaft, toprovide a core stream of air via a second compressor to the combustor,and powering a third shaft using a third turbine of the closed loopsystem that is coupled to the third shaft, to provide power to a fanassembly that provides both the core stream of air to the secondcompressor, and to provide a cooling stream of air to the heat rejectionheat exchanger.

All terms used in the claims are intended to be given their broadestreasonable constructions and their ordinary meanings as understood bythose knowledgeable in the technologies described herein unless anexplicit indication to the contrary in made herein. In particular, useof the singular articles such as “a,” “the,” “said,” etc. should be readto recite one or more of the indicated elements unless a claim recitesan explicit limitation to the contrary.

What is claimed is:
 1. A gas turbine engine, comprising: a first shaftcoupled to a first turbine and a first compressor; a second shaft offsetaxially from the first shaft, the second shaft coupled to a secondturbine and a second compressor; a heat rejection heat exchangerconfigured to reject heat from a closed loop system to bypass air of thegas turbine engine; a combustor configured to combust air from thesecond compressor; wherein the closed-loop system: includes the firstand second turbines and the first compressor; receives energy input fromthe combustor; and provides power from the combustor to the first andsecond turbines.
 2. The gas turbine engine of claim 1, wherein the firstand second shafts are coaxially aligned with one another.
 3. The gasturbine engine of claim 1, wherein the closed-loop system includescarbon dioxide as a working fluid.
 4. The gas turbine engine of claim 1,further comprising a third shaft coupled to a third turbine and a fanassembly, wherein the bypass air is passed from the fan assembly toprovide cooling to the heat rejection heat exchanger.
 5. The gas turbineengine of claim 4, further comprising a gear coupled to the third shaftthat reduces a rotation of a fan blade within the fan assembly relativeto a rotational speed of the third shaft.
 6. The gas turbine engine ofclaim 4, further comprising an inner housing that houses at least aportion of the first, second, and third shafts, and passes airtherethrough from the fan assembly to the combustor, and the bypass airpasses from the fan assembly and the bypass air passing externally tothe inner housing to provide cooling to the heat rejection heatexchanger.
 7. The gas turbine engine of claim 4, further comprising afourth shaft having a fourth turbine and a second fan assembly coupledthereto, and a baffle positioned between the inner housing and an outersurface of the gas turbine engine, wherein: the closed-loop systemincludes the fourth turbine; and the second fan assembly provides:bypass air as thrust air that passes between the baffle and the innerhousing; and cooling air.
 8. The gas turbine engine of claim 1, theclosed loop further comprising a recuperative heat exchanger thatexchanges heat from the working fluid between an outlet of the firstturbine and an input to the combustor.
 9. A method of providing power isa gas turbine engine, comprising: powering a first shaft via a closedloop system that passes a working fluid from a first compressor to acombustor, receives power from combustion in the combustor, passes theworking fluid from the combustor to a first turbine, and cools theworking fluid with bypass air in a heat rejection heat exchanger;passing the working fluid from the combustor and powering a second shaftusing a second turbine of the closed loop system that is coupled to thesecond shaft, to provide a core stream of air via a second compressor tocombust the core stream of air in the combustor; and passing the workingfluid from the combustor to provide power to a fan assembly thatprovides both the core stream of air to the second compressor, andprovides a cooling stream of air to the heat rejection heat exchanger:wherein the closed-loop system: includes the first and second turbinesand the first compressor; receives energy input from the combustor; andprovides power from the combustor to the first and second turbines. 10.The method of claim 9, wherein the first shaft and the second shaft arecolinear with one another.
 11. The method of claim 9, wherein theclosed-loop system includes carbon dioxide as a working fluid.
 12. Themethod of claim 9, further comprising powering a third shaft using athird turbine of the closed loop system that is coupled to the thirdshaft.
 13. The method of claim 12, further comprising operating thefirst, the second, and the third shafts separately and at differentspeeds from one another.
 14. The method of claim 12, further comprisingoperating a gear that is coupled to the third shaft that reduces arotation of a fan blade within the fan assembly relative to a rotationalspeed of the third shaft.
 15. The method of claim 12, further comprisingpassing air through an inner housing that houses at least a portion ofthe first, second, and third shafts, and from the fan assembly to thecombustor, and passing the bypass air from the fan assembly and thebypass air that passes externally to the inner housing to providecooling to the heat rejection heat exchanger.
 16. The method of claim 9,wherein the gas turbine further comprises a fourth shaft having a fourthturbine and a second fan assembly coupled thereto, and a bafflepositioned between the inner housing and an outer surface of the gasturbine engine, and the closed-loop system includes the fourth turbine;the method further comprising providing the bypass air via the secondfan assembly and as thrust air that passes between the baffle and theinner housing.
 17. A power-producing device, comprising: an innerhousing for passing a core stream of air, the inner housing houses: afirst shaft coupled to a first turbine and a first compressor; a secondshaft coupled to a second turbine and a second compressor, the secondshaft axially offset from the first shaft; a combustor configured tocombust air from the second compressor; and a heat rejection heatexchanger configured to reject heat from a closed loop system to bypassair that is passed from a fan assembly; wherein the closed-loop system:includes the first and second turbines and the first compressor;receives energy input from the combustor; and provides power from thecombustor to the first and second turbines.
 18. The power-producingdevice of claim 17, wherein the first shaft is colinear with the secondshaft.
 19. The power-producing device of claim 17, wherein theclosed-loop system includes carbon dioxide as a working fluid.
 20. Thepower-producing device of claim 17, wherein the inner housing furtherhouses a third shaft coupled to a third turbine and a fan assembly,wherein the bypass air is passed from the fan assembly to providecooling to the heat rejection heat exchanger, and wherein the first, thesecond, and the third shafts are separately operable at different speedsfrom one another.